Patent GB-190817209-A (GB)
Title: Improvements in Telephone Exchange Systems and Apparatus therefor.
Inventor: KINGSBURY JOHN EDWARD
Filed: 1908-08-15
Granted: 1909-07-29
Abstract: 17,209. Kingsbury, J. E., [Western Electric Co.]. Aug. 15. Telephone systems.-In an automatic-exchange telephone system, one or more pairs of contact-arms normally traverse constantly past the terminals of the line-wires, the arrangement being such that when the arms engage the earthed terminal of a calling subscriber one arm is caused to remain in contact with these terminals, while by means controlled by the subscriber the other arm is afterwards carried on until it engages with the contact terminals belonging to the line to be called. Each pair of contact-arms thus corresponds with the answering and calling plugs used in manual exchanges. The switches, relays, &c. that are individual to each subscriber in ordinary automatic exchanges are thus dispensed with, and in systems for a small number of subscribers the whole of the multiple wiring is rendered unnecessary, since the line-wires of all the subscribers are simply connected to terminals within reach of all the pairs of contacts-arms used for interconnecting the lines. Certain features of the invention are stated to be applicable in other exchange systems, for example, the means by which a calling subscriber is selected by, and connected to, the rotating contact-arm. Construction of exchange switching-mechanism. Fig. 3 shows the general construction of the switching-mechanism at an exchange for fifty subscribers, and Fig. 5 is an enlarged view of a single pair of contact-arms. Each subscriber is represented by four terminal rods d<1>, d<2>, d<5>, d<6> rigidly fixed in the blocks d, which are pivotally connected to the top and bottom of the cylindrical casing of the switchboard in such a way that, when a subscriber is engaged, his terminal set is moved on its pivots so as to prevent interruption and so as to bring a terminal connected to the "busy" generator into such a position as to give a " busy " signal to any subscriber who attempts to call him. A central rotating shaft r<13> carries six pairs of contact-arms E, F arranged along different radii. Each of these contact-arms carries two electromagnets g, hand k, l, of which the magnets h, k are adapted, when energized (1) to withdraw keys h<8>, k<8> from slots in the collars r<21>, r<22> on the shaft r<13> and thus disconnect the arms E, F from the rotating shaft, and (2) to thrust outwards insulated forked anchoring-arms h<11>, k<11>, which clamp their respective arms to fixed points in the surrounding cylinder of terminal groups. Additional armatures h<9>, k<9> control contacts the function of which will appear later. The magnets g, l actuate switch springs, which complete connexion between the circuits of their respective arms and the groups of line terminals on which they rest. In operation the arms E, F are normally keyed to the rotating shift r<13> and continue to rotate until the wiper e<3> engages the earthed terminal of a calling line, when a circuit is established through the magnets h, k, which thereupon disconnect the arms E, F from the rotating shaft and cause the forked anchoring-arms h<11>, k<11> to engage terminal rods diametrically opposite to the terminals of the calling line. By the action of the calling subscriber the lower arm F is then set in motion again to select the subscriber wanted, the relative movement between the two arms causing a toothed wheel m<1> on the lower arm to interrupt intermittently the contact m<8> on the upper arm and thus control the selection of the called subscriber as described later. Electrical connexion between the two arms E, F is effected by brushes carried by the upper arm bearing upon concentric contact-rings on the upper face of the toothed wheel m<1>. The terminal rods d<1>, d<2> of each group of rods are connected to the line-wires of the respective subscribers, the rod d<5> being earthed and the rod d<6> connected to a "busy" generator. The rod d<5> is electrically connected to a series of ground rings d' adapted to be engaged by the wipers e<4> on the arms E. The rod d<6> is connected to a similar series of "busy" rings d<3> fixed to, but insulated from, the rod d', which rings co-operate with " busy test springs f<3> on the arm F. Sub-station transmitter. The subscriber's interrupter is not designed to send directly to line a predetermined number of impulses, but is constructed so as to close a circuit over one line and earth until a predetermined number of impulses sent from the exchange (by the action of the toothed wheel m<1> and contact m<8>) has returned the pointer of the transmitter to its zero position, when the circuit is permanently broken. The shaft a<3>, Fig. 2, of the interrupter carries a spur-wheel a<5> geared to a star-wheel a<7> adapted to be rotated by the escapement-lever a<8> carried by the armature of the magnet a<11>. The commutator a<13> has a groove in which one member of the switch-springs a<15> normally rests. On turning the pointer a<4> by hand to the number of the line wanted, the switch a<15> is closed, and is only opened when the shaft a<3> has been turned back to its zero position by current-impulses sent through the magnet a<11>. The armature a<20> of an auxiliary magnet a<21> carries a push-button a<19>, so arranged that the circuit of the magnet is completed by the spring a<17> on depressing the button a<19>, which is then held in its depressed position by the magnet. General operation. When a calling subscriber A, Fig. 15, removes his receiver preparatory to making a call, his line-wire 2 is earthed over the resistance c<4> and the armature of the relay c. When the test-spring e<3> of the rotating arm E engages the advanced grounded terminal d<2> of the calling line, current flows from the earthed battery p through the magnets h, g, contact m<8>, wire 8, contact f<5>, e<5> (closed as long as the arm E rotates with the arm F), spring e<3>, and line-wire 2 to earth at the substation. The energizing of the magnet h disconnects the arm E from the rotating shaft, and thrusts the fork h<11> into engagement with the pivot rod of the group of terminals immediately opposite the terminals of the calling line, thus arresting the movement of the arm E. At the same time the magnet g thrusts its contact springs e', e' into engagement with the line-terminals d', d' of the calling line, the oscillation of the group of terminals about its pivots causing the " busy tone ring d<3> to be advanced into the path of the springs f<3> on other contact-arms, so as to prevent interruption from other calling subscribers. The operation of the magnets g, h is made more reliable by means of the local circuit 12, which is closed by the quickacting armature h<9> and is again opened at contact h<14>, when the armature h<2> disconnects the arm E from the rotating shaft. As soon as the contacts d<1>, e<1> engage, a complete metallic circuit is formed and part of the current which passed from the battery p through the magnets h, g, line 2, and resistance c<4> to earth is diverted and passes through the hookswitch and winding c<3> of the relay c, contact a<17>, line-wire 1, contacts d<1>, e<1>, magnets k, l, spring e<4> to the ground terminal-ring d<4>. The energizing of the relay c removes the earth connexion from the line-wire 2. The magnet k disconnects the arm F from the rotating shaft and thrusts the fork k<11> into engagement with the opposite terminal rod, the action of the magnet being rendered reliable by a local circuit 13 similar to the circuit 12 of the arm E. The excitation of the magnet l is prevented by a low-resistance shunt passing to earth by the wire 14, " busy " test spring f<3>, " busy " ring d<3>, and the secondary n<2> of a " busy " transformer. The calling subscriber now revolves the pointer a<4> of his interrupter from his own number (against which it normally rests) to the number of the subscriber wanted, and then depresses the push a<19>, which interrupts at a<17> the metallic line-circuit and earths the line-wire 2 through the magnets a<21>, a<11>. The interruption of the metallic circuit de-energizes the magnet k, so that the arm F is again connected to the rotating shaft, and the relative movement between the two arms E, F now causes the toothed wheel m<1> to open intermittently the circuit through the magnets h, g, a<21>, a<11> of which the magnets h, g, a<21> aro sufficiently sluggish not to be affected, but the magnet a<11> steps round the shaft of the interrupter until it is returned to its zero position, when the earth circuit is permanently broken. The consequent de-energizing of the magnet a<21> again completes the metallic circuit, energizing the magnet k as before, which arrests the arm F opposite the terminals of the subscriber wanted. If this subscriber is engaged, his group of terminals will be oscillated on its pivot so as to thrust the "busy" tone ring d' into engagement with the "busy" test spring f<3>, thereby shunting the magnet l as described above so that the arm will be prevented from thrusting its contact-springs f<1>, f<2> into engagement with the terminals d<1>, d<2>. At the same time the intermittent currents from the transformer n pass to the calling station and give the " busy signal. If the subscriber wanted is disengaged, the magnet l is energized and thrusts the springs f<1>, f<2> into engagement with the terminals d<1>, d<2>, thereby oscillating the group of terminals and bringing the "busy" ring d<3> into its advanced position so as to prevent interruption by other subscribers. This movement of the group of terminals does not cause the magnet l to be short-circuited because the forward thrust of the springs f<1>, f<2>, f<3> causes the spring f<3> to open its contact with the pin f<4>. Continuous calling current now flows from the battery p over the wire-line 1 to the continuous-current bell b and the armature of the relay c to ground. When the called subscriber removes his receiver, this current passes through the winding c<3> of the relay c, which cuts out the bell b.